JANUARY 8, 1925
TABLE II.—Power C
Airspeed =
R.P.M.
290
580
885
1,190
1,400
1,775
2,260
2,810
3,140
3,475
= 0.
Watts.
60
10-0
11-5
190
24 0
27-0
40-1
51 -8
680
89-2
— Consumption of Circular Cylinder.
Airspeed =
R.P.M.
1,020
1,115
1,240
1,500
1,700
1,900
2,080
2,220
2,300
2,420
2,500
2,600
2,700
3,000
15 m/s.
Watts
14-5
15-5
17-3
23-8
26-0
28-4
31-8
28-6
30-2
31-9
33-6
34-8
37-2
44-8
axis, i.e., the resultant air force was assumed to act in this
plane. The dimensions of the set-up were such that a factor
1 • 965 had to be applied to the measured forces to give true
forces acting on the cylinder. Coefficients were derived on a
basis of projected area of the cylinder as follows :—
-. ' V c » ::.r'i:V%C-
• .• .-••_—• . qS • ••••.-.- ••->:• >:;:
Ccw = CWF
Vj1
The first test on the compound strut, in which the gap
between cylinder and fairing was J- in., showed this com-
bination to be inferior to the circular cylinder when con-
sidered as an airfoil. A large scale effect was also found,
coefficients for a fixed ratio of peripheral speed to air speed
varying with the air speed. Tests with a f-in. gap were made
next, but such a large increase of drag was found that no
further combinations were tried.
After the completion of the force measurements, apparatus
was installed to allow the introduction of smoke filaments into
the air stream just in front of the cylinder, and a series of
photographs were taken at various combinations of rotative
and air speeds.
Reduction of Data—Presentation of Results
The air forces acting on the cylinder were assumed to be
symmetrical about a horizontal plane through the tunnel
wherein q is the dynamic pressure, S the projected area of the
cylinder, D the drag force, CWF the cross wind, or " lift "
force, V1 the peripheral speed and V the air speed.
The data from tests on the circular cylinder are given in
Tables I and II. Fig. 4 is a vector diagram which shows the
variations of resultant as well as component forces throughout
the range explored, Fig. 5 indicates the variation of cross-wind
force with the ratio of peripheral to translational speed, and
Fig. 6 shows the power necessary for rotation at zero and
15 m./s. (49-2 ft./sec.) air speed. Corresponding data on the
cross cylinder are given in Tables III and IV [not published—
ED.J ; Figs. 7, 8 and 9 are the vector diagram, plot of cross-
wind force against speed ratio, and power consumption
against revolutions per minute respectively. The data taken
on the compound strut with £ in. gap are given in Tables V
and VI [not published] ; Figs. 10, 11 and 12 are plotted
therefrom. Results from the second strut combination are
given in Table VII [not published] and plotted in Figs. 13
and 14.
Discussion
As no mathematical or physical analysis of the results has
been attempted, as yet, this discussion will, necessarily,
10
9
8
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Airspeed 5 m/s
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100
80
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Air•speed 0 n
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12 16 20 24 28 32 36
R.PM/100
O4 0-8 12 16 20 2-4 28 32 36• .r
6
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O Airspeed 10 m/s
/5 ••
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Rotation
Wind . 'MZ
direction "W
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n
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0 0-2 04 0-6 0# 10 1-2 14
O Airspeec
m "
"> mis
/5 •
c
I IG
B5U
/ r
a
140
120
100
00
60
40
20
1
Air
1
0 /0 m/s
j
f/
p
"7
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1)h
c
i i
8 12 16 20 24 28R.PM/100
0-4 08 1-2 1-6 20
r
TESTS OF ROTATING CYLINDERS : Fig. 4 is the vector diagram in which the lift and drag coefficients
have double the value of the corresponding British " absolute " units. The maximum L/D occurs where
the tangent touches the curve and reaches the value of 7 8. Fig. 5 shows lift coefficient on basis of r,
which is ratio of rotational to translational speed. In Fig. 6 the curves show the power required to rotate
the cylinder in still air and in a wind speed of 15 metres per second. It will be noted that less power is
required to rotate the cylinder in moving than in still air. Figs. 7, 8 and 9 give corresponding curves for
the cross-cylinder. It will be noted that these are somewhat erratic.
..,. _, ,_ . • l& '